1. Field of the Invention
This invention relates to a sheet-like material having excellent fire resistance and bending workability, to a heat-insulating material derived therefrom and to methods of manufacturing same.
2. Description of the Prior Art
The recent search for energy saving devices has promoted the use of various types of heat-insulating materials for a wide variety of applications. They include organic foams, such as polyurethane or polystyrene foam, which are seriously defective in fire resistance. A heat-insulating material composed of inorganic fibers, such as glass fibers or rock wool, is mainly used for a building or facility which is exposed to the danger of a fire. These inorganic heat-insulating materials, however, usually contain no binder, or only a very small quantity of phenol resin which adheres non-uniformly to the inorganic fibers. They are, therefore, very fragile, and difficult to handle, though they are excellent in heat-insulating properties. They are unusable for a corrugated roof, or any other application involving rough handling. For use in any such application involving rough handling, therefore, there has been proposed a sheet-like material compound of inorganic fibers joined together by various types of binders, and having a thickness of, say, 5 to 25 mm, and an appropriate degree of bending workability. All of these sheet-like materials have, however, hitherto been manufactured by a dry process. They contain only a small quantity of a binder which fails to uniformly cover the surfaces of inorganic fibers. They have an intermediate layer in which no binder is present. Accordingly, the sheet-like materials hitherto do not improve the inherent brittleness of inorganic fibers. They are, for example, unusable for the heat insulation of a corrugated roof, since the fibers are crushed and broken when they pass through corrugating rolls.
A wet process for preparing a sheet of paper or board from inorganic fibers has been widely used in the manufacture of glass or asbestos paper, rock wool ceiling boards, asbestos slated, or the like. All the products of the conventional wet process in paper or board form, however, contain only a small quantity of a binder. The products in paper form are brittle, low in bending workability, thin, and deficient in heat insulating properties, though they are flexible. The boards lack flexibility, and are brittle and inferior in heat insulating properties, and unusable for a corrugated roof, or the like, though they are satisfactory in strength. In order to improve these defects, Japanese Patent Publication No. 43485/1974, for example, has proposed a wet process for making a sheet-like material by dispersing rock wool with the aid of a specific surfactant. The mere improvement of dispersibility of rock wool is, however, insufficient for drastically improving the basic properties of a sheet-like material. Moreover, the proposed process does not provide any solution to the breakage of inorganic fibers, since it utilizes an opening and dispersing machine which is used in a conventional papermaking process employing a pulp material, such as a pulper or beater. The sheet-like material obtained by the proposed process is nothing better than a paper-like material.